George Lucas is a good storyteller, he's just a bad director. He gets **** on (probably more than he deserves) for the prequels, but the actual story itself isn't the problem. It's the execution of that story (acting and dialogue mostly) that's the problem. You give the actual story in those films to a competent director and they'd be pretty good films.
Lucas is a good worldbuilder, but he's a terrible storyteller. ESB and ROTJ were credited to other writers in addition to Lucas. ANH has only Lucas as its sole writer credit, but comments from Lucas himself indicate that he had multiple people contribute to at least a half-dozen revisions to his original script, including heavier contribution by the co-writers he had on American Graffiti, especially to the dialogue (which Lucas has said is the weakest part of his writing, and has been substantiated by most of the ANH principle cast. Especially Harrison Ford, who was given latitude to improvise on-set because he was exceptionally vocal about how awful the dialogue was, including an oft-quoted comment he made to Lucas: "George, you can type this ****, but you sure can't say it.")
Just look at the prequel trilogy. By this point Lucas had complete auteur license and could do whatever he wanted. So he was the voice for the movies (Eps 1 and 3 had no other writer credits. Attack of the Clones had a co-writer credit for a guy who was a frequent Lucas collaborator on Indiana Jones material ) and for the most part the thing that gets savaged about the prequel trilogy is the terrible dialogue and character interaction.
Lucas is the guy that makes the sandbox, and it's a great sandbox, no doubt about it. But He's best served by other people playing in it. Or at the very least having someone there to save him from himself.
In actuality, he's a lot like Gene Roddenberry in that regard.
